Siamese‐Twin Porphyrin Origami: Oxidative Fusing and Folding

Oxidation of a nonaromatic Siamese‐twin porphyrin, a pyrazole‐containing expanded porphyrin with two porphyrinlike binding pockets, with a stoichiometric amount of the two‐electron, two‐proton oxidizing agent 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzochinone led to the formation of a single N^pz‐C^o‐Ph linkage between the pyrazole unit with a neighboring meso‐phenyl group, forming a pyrazolo‐ 1,5‐a]indole moiety. Repeated treatment with a second equivalent of the oxidant yielded a doubly N‐fused species, involving the second pyrazole moiety. The conversion products were characterized by variable‐temperature and multinuclear 1D and 2D NMR spectroscopy. The fusions strongly alter the conformation of the macrocycles, as shown by X‐ray diffraction analyses of all three compounds, eventually leading to a folded structure. UV/Vis and NMR‐spectroscopic investigations indicated the presence of highly delocalized but nonmacrocycle‐aromatic π systems. This behavior of the Siamese‐twin porphyrin in response to oxidation is in contrast to the behavior of related all‐pyrrole‐based expanded macrocycles that switch, by redox processes and protonation, between Hückel and Möbius aromatic states.